The present invention relates to the field of automatic test equipment for the testing of electrical units, and more particularly and to an improved automated digital word generating and receiving test device (DWG/R) having several important advantages over those previously in use.
In U.S. Pat. No. 3,832,535, assigned to the assignee of the present invention, the application described apparatus for generating multi-bit digital words, for applying them to an electrical unit under test, and for receiving, for analysis, electrical responses from the unit under test. Prior to the advent of equipment like that disclosed in the patent, digital computers were used in the automated testing of electrical units to generate the digital word patterns to be applied to the unit under test and also for the receiving, for analysis, of the responses of the unit under test. This was not an entirely satisfactory testing method, since a digital computer is not capable of generating test signals in a faster sequence than its cycle time, and since, consequently, it is not capable of effectively testing electrical circuits which have operating frequencies significantly higher (faster) than the computer's access times.
The DWG/R described in U.S. Pat. No. 3,832,535 overcame problems mentioned above by providing a testing device: capable of: (1) generating and applying multi-bit digital words as test signals to the terminals of a unit under test in sequences rapid enought to adequately test extremely high frequency electrical units; (2) capable of receiving for analysis the electrical responses of units under test, and (3) capable of performing these functions independently of a digital computer speed.
Nevertheless, it was recognized that certain testing requirements were left unfulfilled because the lack of a truly practical solution, considering the difficulty of implementing all necessary testing functions and permutations thereof in a comprehensive system.
For instance, many electrical circuits comprise both high and low frequency electrical components which electrically interact in the routine operation of the circuits. In order to meaningfully test these components using a digital word generating device in a realistic environment, stimulus digital word signals should be applied to both high and low frequency components simultaneously, but the rates at which the digital words are applied to the high and low frequency electrical components (i.e. bits per unit time) should reflect the difference in frequency response time characteristic of the electrical components. The ability to test in this way has become even more important with the development of microprocessor technology since it would allow realistic automated digital word testing of microprocessor boards which comprise many electrical components which greatly vary in electrical characteristics including frequency response time.
In addition, some circuits (e.g., some microprocessor circuits) have components which in their operation electrically clock other circuit components. Moreover, such circuits often include a number of components which are internally clocked at different rates. To duplicate this situation in the automated digital word testing environment, and thus test realistically, multi-bit digital words must be applied simultaneously to such circuit components in the different clocked sequences used in the actual operation of the circuit.
Also, prior to this invention, there was a need for automatic testing apparatus capable not only of performing the digital word generating, applying and receiving functions, but also of monitoring a unit under test pin to which a digital test signal has been applied. Such a monitoring capability is highly desirable since, as those skilled in the art are aware, certain electrical units which may be tested, e.g., a bi-directional bus of a microprocessor, may generate response signals at a terminal within an extremely short period of time after a test signal has been applied; unless the testing device is able to monitor the terminals of the unit under test, this "quick" response signal may go undetected and may not be received for analysis.
In addition, it is believed that there was, prior to this invention, a need for an automated digital word testing apparatus which is capable of applying simultaneously multi-bit digital signals to the pins of a unit under test, which may differ in voltage level according to the dictates of a test program or an operator. As the components of an electrical circuit to be tested may differ in voltage response characteristics, this capability is also very desirable in an automated testing facility.
Further, it is believed that there was a need, prior to this invention, for a moderately priced multiple programmable pulse clock system for use in an automated digital testing apparatus capable of accurately regulating with high resolution the application of digital test signals to the terminals of a unit under test in accordance with computer signals, the previous responses of the unit under test or other stimuli.
It is therefore a general object of the present invention to overcome the cited difficulties and fulfill the needs mentioned by providing a device having all of the desirable testing abilities noted above.
A particular object of the invention is to provide a highly flexible and adaptable digital word generating and receiving device capable of applying simultaneously in variable clocked sequences multi-bit digital word testing signals, each of which may vary in voltage level, to the pins of a unit under test, and thereby capable of performing automatically a wide variety of tests.
A further object of the present invention is to provide a digital word generating and receiving device capable of monitoring the pins of a unit under test so that virtually all significant electrical signals emitted at the pins of a unit under test in response to test signals will be detected and received for analysis, including those response signals emitted by very quick response (high frequency) electrical units.
Another object of the present invention is to provide a multiple programmable pulse clock system for use in an automated digital word testing apparatus capable of accurately regulating with high resolution the application of digital signals of a unit under test in accordance with computer commands, previous responses of the unit under test or other stimuli. It is a further object of the invention to provide such a pulse clock system at a moderate cost.